1. Field of the Invention
The present invention relates generally to a method of and an apparatus for successively forming slide-fastener coupling elements by transversely cutting or slicing a continuous metal wire having a substantially Y-shaped cross section. More particularly, this invention concertos such a slide-fastener coupling element forming method and apparatus in which simultaneously with the cutting, a cut edge of the metal wire is chamfered.
2. Description of the Prior Art
In the manufacture of a slide-fastener coupling element of the type concerned, a metal wire that has been preformed into a Y profile in transverse cross section is fed intermittently. While the metal wire is at rest, a cutoff punch and a cutoff die are relatively moved to cut or slice the metal wire into a succession of blank pieces each having an individual product thickness. Subsequently, the head portion of each of the sliced blank pieces is shaped by a pocket-forming punch and a head-forming die into a coupling head having, on its opposite sides, a protrusion and a corresponding pocket. Thus, each blank piece is shaped into a finished coupling element. The finished coupling elements thus produced are collected and after an additional finishing process, such as polishing or plating, they are attached by clinching to a fastener tape along one longitudinal edge thereof. Alternatively, the attachment of the finished coupling elements to the fastener tape may be achieved immediately after the head-forming process described above.
In general, the sharp edges on the press-formed, metal, slide-fastener coupling elements may scratch the user's finger and tend to hinder smooth movement of a slider in the fastener opening and closing directions. To avoid these difficulties, one prior attempt to smooth down the edges of the slide-fastener coupling elements has involved the barrel polishing of the finished coupling elements. According to other prior attempts disclosed in U.S. Pat. No. 3,720,086, edges of the finished coupling elements are partially blunted after the coupling elements are attached to a fastener tape. The blunting process disclosed in the above-mentioned patent publications requires a separate apparatus used exclusively for the blunting purpose and, hence, the whole coupling-element manufacturing system is rendered complicated in construction and the preduction cost of the coupling elements is increased. The prior blunting operation may create flushes on cut end surfaces of the individual coupling elements. Furthermore, since the prior blunting operation is effected only on the leg portions of the coupling elements, the sharp edges on the coupling heads of the respective coupling elements still remain unblunted. With the prior blunting process thus achieved, the coupling elements cannot be smoothly engaged nor disengaged by a slider.
To overcome the foregoing difficulties, the present assignee (i.e. applicant) has proposed an improved method, such as disclosed in Japanese Patent Publication No. 63-11094 (U.S. Pat. No. 4,432,126), wherein a chamfering blade is formed integrally with a cutoff punch at a portion spaced from a cutting edge of the cutoff punch. A metal wire having a substantially Y-shaped cross section is fed intermittently, and while the metal wire is at rest, the cutoff punch and a cutoff die are relatively moved to cut off a blank piece of an individual product thickness from the Y-shaped metal wire. Simultaneous with the cutting, the chamfering blade forms a notch or indent extending in a part of the head portion of the Y-shaped metal wire along the next cutting line of the Y-shaped metal wire. When the next blank piece is sliced off from the metal wire, the edge of a head portion of the thus sliced blank piece is partly chamfered.
The chamfering process disclosed in Japanese Patent Publication No. 63-11094 (U.S. Pat. No. 4,432,126) is effected only at a portion of the peripheral edge of a coupling head of the finished coupling element. The thus chamfered coupling element is successful, as compared with the conventional coupling element having sharp or unchamfered edges, when used in the so-called two-way slide fastener which can be opened and closed in the forward direction or in the reverse direction by a pair of sliders mounted in either face-to-face or tail-to-tail confrontation. However, the coupling elements having such partly chamfered coupling heads are still unsatisfactory to guarantee smooth sliding movement of the sliders.
As is well known in the art, while the slider is moving along a pair of rows of coupling elements, both the coupling head and the legs of each coupling element, and more particularly the peripheral edges at a front end of the coupling head and the outer peripheral edges adjacent to an open end of the legs are brought into sliding contact with the slider. This means that if both of the peripheral edges of the coupling head and the outer peripheral edge of the legs are chamfered, the resulting coupling element will guarantee smooth sliding movement of the slider and provide a smooth touch.